The commit 8811930dc74a503415b35c4a79d14fb0b408a361 ("splice: missing userpointer access verification") added access_ok() to copy_from_user_mmap_sem()which only ensures we can copy the struct iovecs from userspace to the kernelbut we also must check whether we can access the actual memory region pointedto by the struct iovec to close the local root exploit.